Some are time gated behind certain missions and dailys yes, but you should find them in regular rotation in the month. Others you need to complete obscure tasks to get. I can't speak for the other classes apart from Thagomizers in which i helped a titan obtain during the Regicide daily. The AT/S 8 Tarantulas from Bannerfall (killing an enemy near heavy ammo spawn where the tree is with an Ace of Spaces hand cannon) and Shinobu's vow (Using 3x simultaneous flux grenades on the vault door opposite the water pit in Cayde's stash daily for a quest item telling the tale of a cosmodrome huntress turned exo, leading to quest to take down Draksis). Huge credit to the guys on Destiny Raid Secrets reddit btw. [spoiler]Not really. but seriously, just wait[/spoiler]